From Your Link:Yeah, it blows my mind too when I stop and think about how wonderful life is and how things we take as being so concrete are really just our ways of trying to put everything into a nice little box so we can understand them better. To think that simple gene flow from one species to another happens and enables one species however diluted to travel clear across the continent amazes me. Reduced gene flow yes, but not total isolation. http://evolution.berkeley.edu/evosite/evo101/VCCausesSpeciation.shtml
2. Reduction of Gene Flow
However, speciation might also happen in a population with no specific extrinsic barrier to gene flow. Imagine a situation in which a population extends over a broad geographic range, and mating throughout the population is not random. Individuals in the far west would have zero chance of mating with individuals in the far eastern end of the range. So we have reduced gene flow, but not total isolation. This may or may not be sufficient to cause speciation. Speciation would probably also require different selective pressures at opposite ends of the range, which would alter gene frequencies in groups at different ends of the range so much that they would not be able to mate if they were reunited.
This link is about the formation of new species, not about gene flow between species and hybridization. This link has nothing to do with the point you are trying to make.